Method and apparatus for forming metal contacts on a substrate

ABSTRACT

Metal traces and solder bump pads are formed on a semiconductor substrate by way of a semiconductor template that has been micromachined to receive solder paste material. The solder paste material is then formed into precisely controlled ball shapes and metal trace geometries.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 09/708,932,filed Nov. 8, 2000, pending, which is a divisional of application Ser.No. 09/389,316, filed Sep. 2, 1999, now U.S. Pat. No. 6,295,730, issuedOct. 2, 2001.

BACKGROUND OF THE INVENTION

The present invention relates generally to forming contacts on asemiconductor substrate and, more specifically, to the formation ofmetal bump contacts or connectors on a semiconductor substrate usingmicromachining techniques.

Recent advances in data processing devices and memory circuits haveresulted in the implementation of very large scale integrated circuits(VLSI) and even ultra large scale integrated circuits (ULSI). These VLSIand ULSI circuits are fabricated on semiconductor chips that includeintegrated circuits and other electrical parts. In order to mount asemiconductor chip to a carrier substrate, such as a printed circuitboard or a ceramic substrate, solder bumps are arranged onto one of thesemiconductor chips and the carrier substrate so that the semiconductorchip can be mechanically and electrically connected via metallurgicalprocesses by melting the solder bumps.

One approach to applying and forming solder bumps and a carriersubstrate is to use a solder paste. The solder paste is printed onto thecarrier substrate and leads extending from the semiconductor chip areplaced on the solder paste on the carrier substrate. The structure isthen heated to cause the solder in the solder paste to melt so that thesemiconductor chip can be mechanically and electrically connected to thecarrier substrate. To place the solder paste onto the carrier substrate,a metal mask with predetermined openings is typically used. The solderpaste is applied to the surface of the metal mask and a wiper is movedacross the surface of the mask, thus pushing the solder paste throughthe openings of the metal mask onto the surface of the carriersubstrate. Such masks are typically referred to as stencils.

Unfortunately, as the critical dimensions of the integrated circuitsbecome smaller and smaller, the amount of solder paste that can bepressed through a given stencil becomes smaller and the placement of thesolder paste becomes even more difficult. Additionally, with the smallercritical dimensions, the stencil mask becomes even more difficult toclean for a subsequent solder paste application as well as being subjectto high rates of wear because of the constant placement of the stencil,application of the paste to the stencil, and removal and cleaning of thestencil.

Another method of placing conductive contacts for connecting thesemiconductor chip to the carrier substrate has been to use preformedsolder balls that are placed directly upon either the carrier substrateor the semiconductor chip with precisely controlled placement. Once thesolder balls are in place, the solder balls are subjected to heat tocause a partial reflow so that the solder balls adhere to the solderpad. Unfortunately, in this process, as the critical dimensions of thefeatures on the semiconductor chip tend to decrease, significantdisadvantages become apparent in using this type of technique. Onedisadvantage is that the processing costs due to the limited processreliability and the speed of the pick and place nature of the transferprocess become more evident. Another disadvantage is that the physicalhandling and placement of the solder balls by the machine dictates theminimum spacing allowed between solder bumps on a semiconductor chip orcarrier substrate and, thus, requires a semiconductor chip that would belarger than otherwise necessary for the desired VLSI or ULSI circuitry.

Additional problems involve the uniformity of the preformed solderballs. At smaller and smaller ball sizes, the average diameter of thepreformed solder ball may vary greatly from the desired diameter of thepreformed solder ball. This wide discrepancy in uniformity can lead toseveral problems. Preformed solder balls not only cannot be appliedwhere desired, but when a too large or too small preformed solder ballis placed upon a pad, after the formation of a connection using such apreformed solder ball, typically the location will be noted as eitherhaving several bad connections surrounding a ball that is too large orhaving a defective connection where a ball is too small. Large diameterpreformed solder balls tend to prevent adjacent acceptable preformedsolder balls from mechanically and electrically connecting between thecarrier substrate and the semiconductor chip. Small diameter preformedsolder balls are not large enough in diameter to connect to either ofthe two structures since the adjacent acceptable preformed solder ballsare larger in diameter than the smaller ball, which can only touch oneof the two surfaces.

Yet another technique has been developed that uses a method for formingsolder balls on a semiconductor plate having apertures. One suchtechnique is described in U.S. Pat. No. 5,643,831, (the '831 patent)entitled “Process for Forming Solder Balls on a Plate Having AperturesUsing Solder Paste and Transferring the Solder Ball to SemiconductorDevice”, issued Jul. 1, 1997. The '831 patent discloses a method forfabricating a semiconductor device using a solder ball-forming platehaving cavities. Solder paste is placed in the cavities using a solderpaste application, such as a squeegee. Once the cavities are filled withsolder paste, the solder ball-forming plate is heated to form solderballs in the cavities while the plate is in an inclined position. Thesolder balls are then transferred from the plate to a semiconductorchip.

The solder ball-forming plate is fabricated from a semiconductormaterial such as silicon, according to the following method. Initially,a substantially uniform flat surface is formed on the plate. Next, aplurality of cavities is formed in the flat surface of the plate. Thecavities are formed by etching the semiconductor materials after a maskhas been formed on the flat surface, each cavity having the shape of aprecisely formed rhombus or parallelogram.

Yet another example of using a solder ball-forming plate is disclosed inU.S. Pat. No. 5,607,099, (the '099 patent) entitled “Solder BumpTransfer Device for Flip-Chip Integrated Circuit Devices,” issued Mar.4, 1997. The '099 patent discloses a carrier device that has cavitiesformed in its surface for receiving and retaining solder material. Thesolder material can then be transferred to a flip-chip as solder bumps.The cavities are located on the surface of the carrier device such thatthe location of the solder material corresponds to the desired solderbump locations on the flip-chip when the carrier device is placed inalignment with the flip chip. The size of the cavities can be controlledin order to deliver a precise quantity of solder material to theflip-chip. Further, in the '099 patent, the apertures are fabricated sothat they have a width of about 300 μm at the surface of the die and awidth of about 125 μm at its base surface. Meanwhile, in the '831patent, the rhombus-shaped cavities are designed to produce a ball sizeof about 100 μm in diameter. Unfortunately, both of these structurescannot yet produce a ball size for a solder ball that approaches thedimensions currently required in placing a semiconductor chip upon acarrier substrate using the flip-chip technology. Additionally, thesolder ball-forming cavities are limited in shape.

Accordingly, it would be advantageous to overcome the problems ofproducing and using solder balls having uniform sizes as have been shownin the prior art approaches of utilizing preformed solder balls or touse metal masks or stencils to apply solder paste for reflow into solderballs. Additionally, it would be advantageous to make even smaller, moreprecisely formed solder balls than is possible in the prior art as wellas to fabricate metal traces during the same step as that of formingsolder balls using a solder ball-forming plate.

Not only would it be advantageous to overcome the problems of producinguniform solder ball sizes for use in connecting a device to a substrate,but it would also be beneficial to provide a way of greatly improvingthe precision with which solder connections are made in alignment.

BRIEF SUMMARY OF THE INVENTION

According to the present invention, metal traces and solder bump padsare formed on a semiconductor substrate by way of a semiconductortemplate that has been micromachined to receive solder paste material.The solder paste material is then formed into precisely controlled ballshapes and metal trace geometries. First, a semiconductor substrate iscovered with a mask material for protecting selected surfaces of thesubstrate that are not to be etched. Next, a mask is applied in order toanisotropically etch the substrate surface below. Solder ball sites andmetal trace channels are formed at this time. A solder nonwettablematerial is applied to the exposed surfaces of the solder ball sites andthe metal trace channels. A solder paste can then be applied uniformlyacross the surface of the substrate, thus filling in any sites andchannels, or both, that are used to form the desired balls. Thesemiconductor template is then applied solder side to a second substrateso that the solder balls and traces can be applied directly on thesecond substrate, the solder balls being subsequently formed on thesecond substrate by the heating thereof to form the solder paste into asolder ball.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIGS. 1A-D illustrate a cross-sectional view of steps used in formingsolder-receiving holes and channels in a substrate mold according to thepresent invention;

FIG. 2 depicts a surface of the substrate mold having a plurality ofcavities formed therein;

FIG. 3 illustrates the application of solder paste to the cavities andtraces of the substrate mold of FIG. 2;

FIG. 4 depicts the formation of solder bumps in the first substrate moldas mated to a second substrate;

FIG. 5 depicts the second substrate having metal bumps and traces beforefinal reflow;

FIG. 6 illustrates the formation of metal balls on the second substrateafter reflow;

FIG. 7 illustrates a schematic diagram of a mold system using the soldermold according to the present invention;

FIG. 8 depicts a surface of a second embodiment of the substrate mold ofthe present invention having a plurality of hemisphericalcross-sectional shaped cavities formed therein prior to the removal ofthe resist coating on the surface of the substrate mold;

FIG. 9 depicts the substrate mold of FIG. 8 having solder paste in thecavities formed therein in contact with a second substrate;

FIG. 10 depicts the second substrate having the solder paste appliedthereto after the second embodiment of the substrate mold of the presentinvention of FIG. 8 is removed;

FIG. 11 depicts the second substrate of FIG. 10 after the solder pastehas been heated to form solder balls thereon;

FIG. 12 depicts a surface of a third embodiment of the substrate mold ofthe present invention having a plurality of rectangular cross-sectionalshaped cavities formed therein;

FIG. 13 depicts the substrate mold of FIG. 12 having solder paste in therectangular cavities in contact with a second substrate;

FIG. 14 depicts the second substrate of FIG. 13 having the rectangularlyshaped solder paste thereon after having been removed from the substrateof the third embodiment of the invention by the heating thereof;

FIG. 15 depicts the second substrate after the heating of the solderpaste thereon to form solder balls;

FIG. 16 depicts a fourth embodiment of a substrate mold of the presentinvention having a plurality of cavities in a surface thereof and aplurality of heating elements on the other surface thereof;

FIG. 17 depicts the substrate mold of FIG. 16 having solder paste in thecavities formed in a surface thereof; and

FIG. 18 depicts the other side of the substrate mold of FIG. 16illustrating the plurality of heating elements thereon along sectionline 18-18 of drawing FIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

Illustrated in drawing FIGS. 1A-1D is a method for fabricating thesemiconductor substrate to form metal bumps or metal traces, or both, onthe surface of a secondary substrate. A semiconductor substrate,typically a flat planar substrate having a flat planar upper surface, aflat planar lower surface, and a plurality of planar sides forming theperiphery of the substrate, is selected to serve as a bump-formingsubstrate mold 10. The semiconductor substrate may be of any desiredsize and geometric shape suitable for use with an associatedsemiconductor device. The semiconductor substrate is selected from asemiconductor base material such as silicon, gallium arsenide, siliconon insulator, which may include silicon on glass or sapphire, or otherwell-known semiconductor substrate materials, as well as other similartypes of materials, which are capable of being precisely micromachinedand having a coefficient of thermal expansion (CTE) similar to that ofthe semiconductor materials. In this particular application, it ispreferred that a silicon substrate is used for substrate mold 10,although any of the other base materials may be freely substitutedtherefor. The silicon substrate is aligned such that the flat, planarupper surface 12 of substrate mold 10 defines the <100> plane of thesubstrate mold 10 which mates with a semiconductor device (not shown).As is shown in drawing FIG. 1 A, the flat, planar upper surface 12 ofsubstrate mold 10 has a first protective mask layer 14 located thereon.The first protective mask layer 14 serves to protect the surface ofsubstrate mold 10 when a subsequent etch is performed to make thecavities or apertures in the flat, planar upper surface 12. Firstprotective mask layer 14 may be selected from particular etch-resistantmaterials such as nitride, oxide, or a hardened polymer spin-on mask.Substrate mold 10 typically has a thickness of about 25 to 28 mils.

Next, in drawing FIG. 1B, a photoresist 16 is applied over the surfaceof mask layer 14 and then exposed through a mask to define openingsexposing the selected cavity locations to be formed in flat, planarupper surface 12. Then, as shown in FIG. 1C, a sufficient amount ofsemiconductor material is removed by an anisotropic etching from theexposed portion of the flat, planar upper surface 12 after penetrationof the exposed portion of first protective mask layer 14, therebyforming at least one cavity 18. Using an anisotropic etching process,the cavity 18 has walls sloped at 54° relative to the <100> plane of thesubstrate mold 10. The anisotropic etchant may be, for example, KOH, orother etchant materials well known to those skilled in the art. Further,if straight walls are desired, a dry etch using a plasma etch apparatusmay be used to form cavity 18.

After the formation of cavity 18, first protective mask layer 14 isremoved using a dry-etch process that is selective to removing firstprotective mask layer 14 only and not removing any of the underlyingsilicon either in the cavity 18 thus formed or on the flat, planar uppersurface 12 of substrate mold 10. For example, if first protective masklayer 14 is silicon dioxide, a removal substance such as phosphoric acidmay be used. After the removal of the first protective mask layer 14, arelease layer 20 is formed over the entire flat, planar upper surface 12of substrate mold 10, particularly covering cavity 18. Release layer 20is selected from a material that is relatively nonwettable to metalsolder. Such materials include silicon dioxide or silicon nitride, whichcan be applied using a chemical vapor deposition process. Othermaterials that are relatively nonwettable to metal solder may also beused, such as nonwettable polymers or the like. The resulting structureis depicted in drawing FIG. 1D.

Although drawing FIGS. 1A-D illustrate only a single cavity 18, it isintended that a plurality of cavities be formed in an array acrosssubstrate mold 10. An example of a solder ball forming mold or substratemold 10 that has such a plurality of cavities 18 is depicted in drawingFIG. 2. Release layer 20 is applied and utilized to minimize the wettingof solder paste on the substrate mold 10 when the assembly is heated inorder to transfer the solder onto the bumps of the secondary surface.

Solder paste is applied, as shown in drawing FIG. 3, by use of anapplicator 22, such as a squeegee, that is passed across the surface ofsubstrate mold 10, pressing a metal solder paste 24 into the pluralityof cavities 18 and wiping the excess paste away. The solder paste 24fills cavities 18, thus forming frustoconically shaped solder bumps 26(shown in FIGS. 3 and 4).

Various types of metal solder may be used. The most widely employedtypes include a lead-tin combination. Other types of metal solder mayinclude, but are not limited to, lead-silver, lead-tin-silver,lead-tin-indium, indium-tin, indium-lead, or any paste using copper orgold in combination with the lead or tin. For example, a lead-tin solderpaste having a 63/37 weight ratio has a eutectic temperature of 183° C.Another type of lead-tin paste that has a 95/5 weight ratio has aeutectic temperature of about 350° C.

Once the solder paste 24 is applied to flat, planar upper surface 12 ofsubstrate mold 10, the entire assembly is heated to a temperaturesufficient enough to slightly melt the metal solder paste in order tobegin the formation of the solder bumps to be transferred. As shown indrawing FIG. 4, after this partially melted solder state has beenreached, substrate mold 10 is inverted and applied to the surface of acarrier substrate 28, which may comprise a semiconductor device (die),wafer, or flexible substrate, such as a flex tape. The assembly of thesubstrate mold 10 and carrier substrate 28 is heated to a sufficientlyhigh enough temperature to cause solder bumps 26 to slightly reflow andrelease from the release layer 20 formed on substrate mold 10. Substratemold 10 is then removed and solder bumps 26 adhere to bond pads,terminal pads or other conductive, solder wettable sites 30 on carriersubstrate 28, as shown in drawing FIG. 5. Next, an additional reflowstep may be performed that causes solder bumps 26 to form intoapproximately spherically shaped solder balls 32 attached to conductivesolder wettable sites 30 as depicted in drawing FIG. 6.

Because of the generally trapezoidal shape of solder bumps 26, thesolder paste, upon heating reflow, draws into a substantially sphericalshape and is held together by the surface tension of the solder materialto form approximately spherically shaped solder ball 32 or a truncatedspherical ball (not shown).

Although it has been depicted how solder balls or bumps 32 are formed indrawing FIG. 4, it is also possible to form metal traces using substratemold 10. The same type of patterning and etch steps as described withrespect to FIGS. 1A-1B would be followed, but would include a layoutthat would form metal traces or channels.

A solder mold system is depicted in drawing FIG. 7 which incorporatesthe substrate mold 10 shown in drawing FIGS. 1-6. The mold systemincludes solder applicator 22 for spreading metal solder paste 24 asdispensed by metal paste dispenser 52. Once the paste is sufficiently inplace within the cavities 18, the substrate mold 10 is mated to asecondary substrate, as shown in drawing FIG. 4, and then placed in alow-temperature metal paste reflow oven 54 to melt the paste to asufficient enough consistency to form self-supported bumps and hassufficient enough tackiness to wet the conductive gates on the carriersubstrate 28.

Referring to drawing FIG. 8, an alternative embodiment of a substratemold 40 of the present invention is illustrated. The substrate mold 40is similar to the substrate mold 10 described hereinbefore as toconstruction and methods of construction except that the cavities 18formed therein are hemispherically shaped. As illustrated, the firstprotective mask layer 14 used to form the plurality of cavities 18 ispresent on portions of the flat, planar upper surface 42 of thesubstrate mold 40. As with the substrate mold 10, the substrate mold 40may include a release layer 20 to aid in the release of the solder pastecontained within the hemispherical cavities 18.

Referring to drawing FIG. 9, once the solder paste 24 is applied toflat, planar upper surface 42 of substrate mold 40, as described hereinwith respect to substrate mold 10 illustrated in drawing FIG. 3, theentire assembly of the substrate mold 40 and carrier substrate 28 havingconductive sites or bond pads 30 located thereon for the solder paste 24to be applied is heated to a temperature sufficient enough to slightlymelt the metal solder paste 24 in order to begin the formation of thesolder bumps to be transferred.

As shown in drawing FIG. 9, after this partially melted solder state hasbeen reached, the assembly of the substrate mold 40 and the carriersubstrate 28 is inverted so that the solder paste 24 in cavities 18 isapplied to the conductive sites 30 on the surface of the carriersubstrate 28, which may comprise a semiconductor device (die), wafer, orflexible substrate, such as a flex tape. The assembly of the substratemold 40 and carrier substrate 28 is heated to a sufficiently high enoughtemperature to cause solder bumps 26 to slightly reflow and release fromthe release layer 20 formed on substrate mold 40. Substrate mold 40 isthen removed and solder bumps 26 adhere to the conductive sites, bondpads, terminal pads or other conductive, solder wettable sites 30 oncarrier substrate 28, as shown in drawing FIG. 10. Next, an additionalreflow step may be performed that causes solder bumps 26 to form intoapproximately spherically shaped solder balls 32 attached to conductivesites 30 as depicted in drawing FIG. 11.

Because of the generally hemispherical shape of solder bumps 26, thesolder paste, upon heating reflow, draws into a substantially sphericalshape and is held together by the surface tension of the solder materialto form approximately spherically shaped solder balls 32 or truncatedspheres.

Referring to drawing FIG. 12, an alternative embodiment of a substratemold 50 of the present invention is illustrated. The substrate mold 50is similar to the substrate molds 10 and 40 described hereinbefore as toconstruction and methods of construction except that the cavities 18formed therein are generally rectangular, or square shaped (shown indashed lines). The first protective mask layer 14 used to form theplurality of cavities 18 present on portions of the flat, planar uppersurface 42 of the substrate mold 50 is not illustrated. As with thesubstrate mold 10, the substrate mold 50 may include a release layer 20to aid in the release of the solder paste contained within thehemispherical cavities 18. Referring to drawing FIG. 13, once the solderpaste 24 is applied to flat, planar upper surface 42 of substrate mold50, as described herein with respect to substrate mold 10 illustrated indrawing FIG. 3, the entire assembly of the substrate mold 50 and carriersubstrate 28 having conductive sites or bond pads 30 located thereon forthe solder paste 24 to be applied is heated to a temperaturesufficiently high enough to slightly melt the metal solder paste 24 inorder to begin the formation of the solder bumps to be transferred.

As shown in drawing FIG. 13, after this partially melted solder statehas been reached, the assembly of the substrate mold 50 and the carriersubstrate 28 is inverted so that the solder paste 24 is applied to theconductive sites 30 on the surface of the carrier substrate 28, whichmay comprise a semiconductor device (die), wafer, or flexible substrate,such as a flex tape. The assembly of the substrate mold 50 and carriersubstrate 28 is heated to a sufficiently high enough temperature tocause solder bumps 26 to slightly reflow and release from the releaselayer 20 formed on substrate mold 50. Substrate mold 50 is then removedand solder bumps 26 adhere to the conductive sites, bond pads, terminalpads or other conductive, solder wettable sites 30 on carrier substrate28, as shown in drawing FIG. 14. Next, an additional reflow step may beperformed that causes solder bumps 26 to form into approximatelyspherically shaped solder balls 32 attached to conductive sites 30 asdepicted in drawing FIG. 15.

Because of the generally rectangular shape of solder bumps 26, thesolder paste, upon heating reflow, draws into a substantially sphericalshape and is held together by the surface tension of the solder materialto form approximately spherically shaped solder balls 32.

Referring to drawing FIG. 16, another embodiment of the substrate mold100 of the present invention is illustrated. The substrate mold 100 issimilar to the substrate molds 10, 40, and 50 described hereinbefore.The substrate mold 100 includes cavities 18 having any desired shape asdescribed herein in the flat, planar upper surface 12 and includeselectrical resistance heating strips 66 located on the bottom thereoffor the heating of the substrate mold 100 with electrical conductor 68connected thereto. The bottom surface of the substrate mold 100 includesa coating 62 thereon to electrically insulate the heating strips 66 fromthe substrate mold 100. The heating strips 66 may be of any desiredgeometrical configuration to cover the bottom surface of the substratemold 100 to uniformly heat the mold 100 and the solder paste 24 locatedin the cavities 18 thereof. The electrical conductor 68 may be anydesired shape and have any desired location for connection to theheating strips 66. The electrical conductor 68 is covered with aninsulation layer 70 located thereover. In areas or portions of thebottom surface of the substrate mold 100 not having a heating strip 66located thereon, an insulative coating 64 of any suitable type isprovided.

Referring to drawing FIG. 17, the substrate mold 100 is illustratedhaving solder paste 24 located in cavities 18 having release layer 20therein. After the solder paste 24 is placed in the cavities 18, acarrier substrate 28 (see FIG. 4) is applied to the substrate mold 100,the assembly of the substrate mold 100 and carrier substrate 28inverted, and the electrical resistance heating strips 66 on thesubstrate mold 100 actuated to heat the solder paste 24 to transfer thesame to the carrier substrate 28. After the solder paste 24 istransferred to the carrier substrate 28, the carrier substrate 28 isfurther heated to cause the solder paste to adhere to the conductivesites 30 on the carrier substrate 28 to substantially form solder balls32 thereon.

Referring to drawing FIG. 18, the electrical resistance heating strips66 and electrical conductor 68 are illustrated. The heating strips 66may be of any desired shape to substantially uniformly heat thesubstrate mold 100. Similarly, the electrical conductor 68 may be anydesired shape to electrically connect to the heating strips 66. Further,any desired connector may be used to electrically connect the electricalconductor 68 to a source of electrical power.

Substrate molds 10, 40, 50 and 100 described herein are useful informing contact bumps for many applications. One application is theformation of flexible connecting tape that requires bumps forinterconnection of traces on the tape to a die or other element. Themicromachining of substrate mold 10 provides a much more accurate meansfor placing the solder ball shaped bumps over the prior art methods ofmerely placing bumps on top of a screen and then having the screen placethe bumps in a proper alignment. Further, the solder ball shaped bumpshave a more uniform volume and shape as the cavity dimensions in thesemiconductor mold provide a substantially precise control over theformation of the solder ball shaped bumps. By contrast, in the priorart, the uniformity of solder balls has always been a problem,especially at the smaller diameter dimensions that are now being used.Another application for the present invention is for the directplacement of the solder ball shaped bumps on a semiconductor device ordie for attachment. Yet another application includes placing the solderball shaped bumps on a wafer-scale device for interconnection. Thisallows multiple devices placed on the same substrate to beinterconnected using the precision of the solder ball shaped bumps. Forexample, the solder ball shaped bump application is useful in chip scalepackages (CSP) or in fine ball grid array (FBGA) packages. The in situelectrical resistance heating strip allows for selecting which ballsneed to be transferred by selectively heating only those electricalresistance heating strips 66.

The applications of providing interconnect and bump contacts arenumerous. For example, the metal trace interconnect and the bump contactmay be used in any type of semiconductor device such as a memory storagedevice. These memory storage devices can range from read-only memory(ROM) and random access memory (RAM) to exotic types of memory such asvideo memory and the memory used in computer systems. Additionally, theapplication of this metal trace interconnect and bump contact structurecan be utilized in micro-processor packages that are used in computersystems as well as in other types of systems, and other types of singleprocessing devices and support chips normally used in electronicdevices. These electronic devices range from cellular phones tomicrowave systems, to automobiles and even to programmable wristwatches.

Although the present invention has been described with reference to aparticular embodiment, the invention is not limited to this describedembodiment. The invention is limited only by the appended claims, whichinclude within their scope all equivalent devices or methods whichoperate according to the principles of the invention as describedherein.

1. An intermediate solder ball forming apparatus comprising: a moldsubstrate comprising; an upper surface, a lower surface, and at leastone cavity formed in the lower surface of the substrate having a layerhaving a first degree of wettability relative to solder paste; a carriersubstrate disposed below the mold substrate comprising: a surfaceabutting the lower surface of the mold substrate, and at least one bondpad disposed on the surface of the carrier substrate below the at leastone cavity formed in the lower surface of the mold substrate, the atleast one bond pad having a second degree of wettability relative tosolder paste that is greater than the first degree of wettability of thelayer of the at least one cavity; and solder paste disposed within theat least one cavity adjacent the layer thereof, gravity acting on thesolder paste moving it from the layer of the at least one cavity to thebond pad disposed on the carrier substrate.
 2. An intermediate solderball forming apparatus comprising: a mold substrate comprising; an uppersurface, a lower surface, and at least one cavity formed in the lowersurface of the substrate having a layer having a first degree ofwettability for solder paste; a carrier substrate disposed below themold substrate comprising: a surface abutting the lower surface of themold substrate, and at least one bond pad disposed on the surface of thecarrier substrate below the at least one cavity formed in the lowersurface of the mold substrate, the at least one bond pad having a seconddegree of wettability relative for solder paste at least greater thanthe first degree of wettability of the layer of the at least one cavity;and solder paste disposed within the at least one cavity adjacent thelayer thereof for having gravity to act on the solder paste for movingthe solder paste from the layer of the at least one cavity to the bondpad disposed on the carrier substrate.
 3. A solder ball formingapparatus comprising: a mold substrate comprising; an upper surface, alower surface, and at least one cavity formed in the lower surface ofthe substrate having a layer having a first degree of wettability forsolder paste; a carrier substrate disposed below the mold substratecomprising: a surface abutting the lower surface of the mold substrate,and at least one bond pad disposed on the surface of the carriersubstrate below the at least one cavity formed in the lower surface ofthe mold substrate, the at least one bond pad having a second degree ofwettability for solder paste at least greater than the first degree ofwettability of the layer of the at least one cavity; and solder pastedisposed within the at least one cavity adjacent the layer thereof forhaving gravity to act on the solder paste for moving the solder pastefrom the layer of the at least one cavity to the bond pad disposed onthe carrier substrate.